The present invention relates in general to therapies such as stenting. Specifically, the present invention relates to a vascular orientation marker which reduces parallax (radiological foreshortening) and enables the orientation of a blood vessel in a patient to be accurately visualized so that a stent can be accurately placed at the origin of the blood vessel.
Renal artery stenosis most commonly occurs at the junction of the aorta and the renal artery ostium. Lesions located at this junction are called renal ostial lesions. Unlike renal lesions located away from the aortic junction, ostial lesions do not respond well to transluminal renal angioplasty. Renal ostial lesions are technically difficult to dilate and have a high restenosis rate. Angioplasty with stent placement has been shown to have a higher clinical success rate in achieving and maintaining renal artery patency in ostial renal artery lesions.
Presently, when performing a stenting therapy, it is often difficult to determine the actual origin of a blood vessel. For example, the orientation of the renal artery is difficult to accurately determine during ostial renal stenting; which is when a stent is placed at the origin of a renal artery. The renal artery originates at the aorta and comes off the aorta at an angle towards the patient""s back. The location at the aorta and the angle varies depending on the anatomy of each patient.
When a patient is radiographically imaged with the axis of the X-ray at a 90 degree angle to the flat surface on which the patient is lying, the image will not generally indicate the origin of the renal artery.
In particular, FIGS. 1 and 2 illustrate the origin of each of the renal arteries 18 at the aorta 20. If this arrangement is visualized fluoroscopically, the origin of each renal artery is obscured by the aorta.
It is extremely important during renal stenting that a stent be placed so that it covers the zone at the origin of the renal artery. This must be done without extending the stent out into the aorta by more than three millimeters. If the stent is placed extending further out in the aorta, the stent can disrupt aortic blood flow possibly leading to thrombosis. Devices being manipulated in the aorta secondary to stent placement can also disrupt the stent if the stent extends substantially into the aorta.
If the stent is placed too far into a renal artery, the stent will not adequately support the diseased area at the origin of that renal artery. To accurately place a stent at the origin of a blood vessel, and positions along the blood vessel must be visualized and to do so, the orientation of the blood vessel within the patient""s body must be accurately determined.
Accordingly, it is an object of the present invention to provide a device which enables determining the position of the origin of a subsidiary blood vessel, such as the renal artery, relative to the surface of the more primary blood vessel, such as the aorta, off of which the subsidiary blood vessel extends.
It is a further related object of this invention to provide a method to accurately visualize the origin or orientation of a blood vessel within a patient""s body. More specifically, by identifying the origin of the subsidiary blood vessel, enabling the position of an X-ray beam so that its direction of propagation will be perpendicular to the axis of the origin and thus provide a clear radiographic image showing the origin of the blood vessel; thereby permitting procedures, such as the positioning of a stent at the origin, to be accurately undertaken.
The use of radiopaque identifiers during fluoroscopic procedures are well known in the art. These identifiers can be in the form of markers, tape and other scaling devices. Radiopaque markers, spaced at pre-determined distances along the shaft of a catheter, are commonly used to determine the length of diseased segments of vascular structures. These catheters, also known as sizing devices, have no mechanism for ensuring perpendicular alignment between the markers and the X-ray beam. As a result, apparent length measurements may not equal the true length measurements.
U.S. Pat. No. 5,970,119 to Hofmann discloses a radiological scaling device which provides for calculation of sizes and lengths of anatomical structures. The device includes a mechanism for ensuring perpendicular alignment between the scale and the X-ray beam through the use of radio-lucent visualization gaps. The scaling device may be in the form of an externally placed strips, a catheter or adhesive tape. To determine the length or size of an anatomical structure, the apparent length/size of the radiopaque zone is first measured using fluoroscopy. Calculations of the difference between the apparent measured length and the true length of the radiopaque zone are then used to determine the actual length or size of the structure.
The ""119 patent does not address a technique for determining the position of the origin of a subsidiary blood vessel relative to the source of the primary blood vessel off of which it extends. Nor, does the ""119 patent teach or suggest a method for clearly visualizing the origin of a blood vessel so that procedures, such as the positioning of a stent, can be accurately undertaken.
Disclosed is a catheter having one or more radio-opaque bands near its distal end. The catheter is inserted in the renal artery. An X-ray image of the bands is used to determine the position of the renal artery relative to the aorta. This determination facilitates proper insertion of a stent at the origin of the renal artery.
In one presently preferred embodiment, two annular radio-opaque bands are placed at the distal end of the catheter body. On a 0.067 inches (1.70 mm)diameter catheter, the bands are each 0.040 inches (1.02 mm) wide and are spaced from one another by 0.006 inches(0.15 mm). This provides a 0.006 inches (0.15 mm) radio-translucent band bounded by first and second radio-opaque bands.
When the distal end of the catheter is inserted into a renal artery, the radiologist can orient an X-ray machine until the two radio-opaque bands are clearly imaged and differentiated from one another. This means that the X-ray machine is properly aligned relative to the axis of the bands on the catheter and thus the direction of X-ray propagation is perpendicular to the axis of the renal artery. Such alignment provides an image that appropriately identifies the origin of the renal artery. For accurate stent placement at the origin of the renal artery, the physician must be able to determine the renal artery""s take off angle from the aorta within plus or minus five degrees.
A stent may then be placed accurately at that origin because the image provided by the X-ray machine is so oriented that it will show the proximal end of the stent aligned with the origin of the renal artery.
Also disclosed are alternate embodiments of the vascular orientation marker of this invention. These alternate embodiments have various radio-opaque features at the distal end of the catheter employed.
One such example is a single radio-opaque band, which therefore is surrounded by radio-translucent zones. The radiologist can determine appropriate orientation when the single band is imaged as having a uniform minimum image width.
Other embodiments employ a radio-opaque band having radio-translucent portions 180xc2x0 displaced from one another. The X-ray machine is positioned so that these portions are aligned with the axis of projection to provide an image of the radio-translucent portion. This provides an indication of a proper alignment between the X-ray machine and the renal artery.